Chucks usually have a cylindrical base body into which a back-up spindle or the like is screwed. Clamping or holding jaws are axially supported on the back-up spindle, and retained in position by a holding sleeve or the like which surrounds the jaws. Preferably, the holding sleeve includes an essentially cylindrical sleeve element. The holding sleeve and/or the sleeve element are rotatable with respect to the base body. It is known to place between the sleeve and the base body a releasable locking arrangement. The locking arrangement locks when the sleeve is rotated in one direction, and can be unlocked, to release the clamping jaws, when rotated in the opposite direction.
Chucks which operate at high speed, that is, at high revolution of the spindle, which is typical for computer numerically controlled machines, may cause release of the lock, and hence release of the clamping jaws which clamp a tool, such as a drill, a boring tool, a reamer or the like. This may occur, particularly, if the machine is operating at high speed and then abruptly stopped. To prevent such loosening of the locking of the clamping jaws, and hence of the tool upon sudden stopping, a locking arrangement has been proposed to be placed between the base body and the sleeve in form of a ratchet which secures the base body and the sleeve with respect to relative movement in the direction of loosening of the clamping jaws. Of course, the ratchet is so arranged that the tool, and hence the clamping jaws can be tightened; relative rotation in the direction of tightening is not impeded. The selfretaining clamping function of the chuck, upon rotation in working direction, thus is retained. Such an arrangement is described, for example, in the referenced European Published Application No. 0017 748. The arrangement there described utilizes a pressure ring which is secured to rotate with the sleeve and which is axially supported on the base body by the sleeve itself. A spring-loaded ratchet latch is located on the ring which is directly operatively coupled to a gear ring located on the base body. In order to be able to open the jaws, for example in order to change tools or the like, an arrangement is provided to open the latch of the ratchet. This opening arrangement includes a rotatable release ring located at the axially backward end of the sleeve and positioned coaxially to the axis of rotation, and fitting over the ring. The opening release ring has a stop engageable with a suitable end release projection on the latch elements of the ratchet.
Swiss Patent No. 635,766 describes a jaw chuck which also has a circular ratchet ring and, generally, operates similarly to the chuck just described.
A ratchet lock, with a movable ratchet latch element, or a plurality of movable ratchet elements is comparatively complex and large; it requires a not insignificant space on the chuck structure. Due to the nature of the ratchet, it can operate only in steps. Consequently, the locking of the clamping force or effect of the jaws can be obtained only in steps. This is undesirable for many applications. The spacing of the steps is governed by the spacing of the teeth on the gear ring, and the construction of the ratchet, and the latch elements themselves.
German Democratic Republic Patent No. DD-PS 201 985 describes an axially short clamping chuck which has a clamping effect independent of the direction of rotation. The base body which receives the back-up spindle is rotatably located in a conical element which is directly screw-connected to a closing cap. To tighten and, respectively, loosen the clamping jaws, a worm drive is provided between the base body and the conical element to permit relative rotation thereof. The worm can be operated by an Allen wrench externally engageable in a suitable receiving portion of the worm arrangement.
The worm arrangement, however, loses the advantage of a self-tightening function of the rotating chuck. It is inconvenient to require an external separate tool in order to permit tightening of the chuck.